JPH01119306A - Method for washing reverse osmosis membrane - Google Patents

Abstract

PURPOSE:To dispense with special equipment or detergent for washing a reverse osmosis membrane and a drain treatment process accompanying washing, by supplying a low solute concn. liquid to the transmitted water side of the reverse osmosis membrane while supplying a high solute concn. liquid to the raw water side thereof and excluding the contamination layer on the surface of the membrane by the flow transmitting through the membrane based on a positive osmotic phenomenon. CONSTITUTION:When a reverse osmosis membrane is washed, valves 10, 15 are opened and valves 11, 14 are closed. For example, when raw water is used as a high solute concn. liquid and made water is used as a low solute concn. water, the raw water is passed through a line (b), a supply pump 2 and filter 3 from a tank 1 and supplied to a membrane module 5 through a bypass line d' without being passed through a high pressure pump 4 while the made water is supplied to the membrane module 5 through a line (m). In the membrane module 5, transmitted water moves to the outside of the membrane being the raw water side from the inner surface of the membrane by the positive osmotic phenomenon generated by concn. difference and, at this time, the contamination layer bonded to the outer surface of the membrane is released and discharged out of the system along with the raw water and the transmitted water from a concd. water discharge line (i).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a reverse osmosis membrane for a reverse osmosis device that processes seawater, river water, wastewater, etc. with a reverse osmosis membrane for purposes such as desalination or reuse. Concerning a cleaning method.

[Conventional technology]

In general, reverse osmosis membranes (hereinafter simply referred to as membranes) are adversely affected by suspended matter in the liquid to be treated, microorganisms such as bacteria, and dissolved organic matter such as humic acid. That is, the suspended solids adhere to the outer surface of the membrane, forming a contaminated layer, and causing a decrease in the amount of produced water. Additionally, microorganisms erode the membrane and reduce the solute removal rate. Furthermore, dissolved organic matter precipitates on the membrane surface as the solvent (usually water) permeates into the membrane and the solute concentration increases, forming a contamination layer similar to turbidity, resulting in a decrease in the amount of produced water.

Conventionally, as a countermeasure against the above-mentioned effects, a common method has been to add a microbial disinfectant such as chlorine, remove turbidity and dead microorganisms Z from the liquid to be treated using an r-filter, and then supply it to the membrane of the liquid to be treated. be.

However, there are many cases in which a contaminated layer is formed on the membrane surface due to leakage of turbidity (including dead microorganisms) in the r-filter and precipitation of dissolved organic matter on the membrane surface, resulting in a decrease in the amount of water produced. .

In such cases, for example, use a synthetic detergent to clean the membrane surface Z.
A cleaning method is used.

A conventional membrane cleaning method will be explained based on FIG.

First, normal operation, that is, when water generation is performed, will be explained.

Raw water, which is a liquid to be treated, is temporarily stored in a raw water tank 1 through line a. A microbial sterilizer is added to line a at a predetermined concentration from line 1. The raw water in the raw water tank 1 is sent to the feed pump 2 in the line 1, and the feed pump 2 passes the valve in the line 1 and supplies it to the filtration device 3. At this time, valve 8 in line b is open, and valve 9 in line b is closed. r
The filter unit 3 removes suspended matter and dead microorganisms from the raw water.
It is sent to the high pressure pump 4 via line d. At this time, line d
The valve 11 of line d' is open, and the valve 10 of line d' is closed. The high pressure pump 4 boosts the pressure of raw water to a predetermined pressure and supplies it to the membrane module 5 via line e. Membrane mo9. - In Rule 5, manufactured water (usually low solute concentration water is the manufactured water) is obtained depending on raw water properties such as solute concentration and conditions such as pressure and temperature. Manufactured water is recovered from the membrane module 5 through line f, temporarily stored in a manufactured water tank 6, and then supplied through line g to a process requiring the manufactured water. The condensed water is extracted from the membrane module 5 through the line hK, and is further sent to the outside of the yarn through the line 1 via the valve 12. At this time, the line 1 intermediate valve 12 is open, and the line j intermediate valve 13 is closed.

Next, how to clean the membrane! explain.

During cleaning, valve 8 in line b is closed, line middle extension 9 is open, line 1 middle extension 10 is open, line d middle extension 11 is closed, line i middle extension 12 is closed, line j middle extension 13 is closed. Open.

The cleaning liquid is prepared in a cleaning liquid tank 7 and sent to a supply pump 2 through a valve in a line 1. The supply pump 2 serves as a power source for circulating the cleaning liquid, and the cleaning liquid is circulated through the first filter 3, line d', line e, membrane module 5, line h1, and then returned to the cleaning liquid tank 7.

[Problem that the invention seeks to solve]

The conventional membrane cleaning method in which a tank and a pipe are provided separately from the above-mentioned normal operation and a cleaning solution is circulated to remove a contaminated layer adhering to the membrane surface has the following problems.

(1) Additional equipment Z for cleaning other than equipment used for normal operation of tanks, pumps, pipelines, etc. is required.

(2) Cleaning agent is required, and at the same time, used cleaning agent processing process y! -It takes.

(3) The contaminated layer to be removed is originally formed from components contained in the raw water and drawn out, and the contaminated layer is difficult to peel off even if a cleaning agent is poured outside the contaminated layer.

In particular, removal of poorly soluble solids after precipitation is not sufficient with conventional methods.

As mentioned above, the conventional cleaning method requires new and separate equipment, which not only increases the equipment cost (but also has the problem that the cleaning effect is not sufficient).

The present invention was developed in view of the current situation, and is a method for cleaning reverse osmosis membranes that does not require special equipment or cleaning agents for membrane cleaning, and does not require a wastewater treatment process associated with cleaning. The purpose is to provide a method.

[Means for solving problems]

The present invention provides a reverse osmosis device for desalination or wastewater reuse using a reverse osmosis membrane, in which a low solute concentration solution is supplied to the permeated water side of the reverse osmosis membrane, while the raw water of the reverse osmosis membrane is The reverse osmosis method is based on the forward osmosis phenomenon that occurs through the reverse osmosis membrane by supplying high solute concentration liquid to the side and eliminates the contaminated layer on the reverse osmosis membrane surface by the flow that passes through the reverse osmosis membrane. This paper proposes a method for cleaning permeable membranes.

[Effect]

The method of the present invention utilizes forward osmosis, a phenomenon in which a solvent (usually water) moves from a low solute concentration side to a high solute concentration side, to remove the contaminated layer adhering to the membrane surface.

In other words, the permeated water side of the reverse osmosis membrane is low solute concentration water (manufactured water may be used) that does not affect the membrane in the manufactured water line, for example, which is not clogged with turbidity, and - the raw water side of the reverse osmosis membrane. By continuously or intermittently supplying high solute concentration water (either raw water or concentrated water) to the concentrated water line or raw water supply line, a flow of permeated water based on the forward osmosis phenomenon is generated inside and outside the membrane, resulting in a low The water in the solute-concentrated water, that is, the permeated water, is transferred to the high-solute-concentrated water through the membrane χ.

In this way, the permeated water, which becomes cleaning water, moves from the inside of the membrane to the outside of the membrane, which is the raw water side, so that the contaminated layer attached to the outer surface of the membrane can be efficiently peeled off and removed. The fact that the method of the present invention is effective in removing the contaminated layer can be understood from the fact that the contaminated layer is formed on the outer surface of the membrane.

Furthermore, according to the method of the present invention, the flow rate (flow rate) of permeated water, which becomes cleaning water, can be adjusted by changing the solute concentration, so the scale of cleaning can be set according to the degree of formation of a contaminated layer. .

Furthermore, the method of the present invention not only requires almost no equipment such as tanks and pumps associated with cleaning, but also does not require a cleaning agent and does not require a cleaning agent processing step, resulting in a reduction in equipment costs.

The mixed water of the forward osmosis permeate and high solute concentration water is discharged from the system through the raw water supply line or the concentrated water line.

〔Example〕

One embodiment of the present invention will be explained in detail based on FIG.

In addition, the parts in FIG. 1 having the same reference numerals as those in FIG. 2 indicate the parts having the same functions as the parts shown in FIG. 2.

In FIG. 1, raw water, which is a liquid to be treated, is temporarily stored in a raw water tank 1 through line a. A microbial sterilizer is added to line a at a predetermined concentration from line 1. The raw water in the raw water tank 1 is supplied to the supply pump 2 via line b, and the supply pump 2 supplies it to the "'C filter 3 via line C. In the filter 3, turbidity and dead matter in the raw water are removed. After removing the microorganisms, the raw water is passed through line d to high-pressure pump 4.
send to At this time, the line d' intermediate extension 10 is closed. In the high pressure tube 4, the raw water is pressurized to a predetermined pressure and is supplied to the membrane module 5 via the line e. In the membrane module 5, manufactured water is obtained depending on the properties of raw water such as solute concentration, and conditions such as pressure and temperature. The manufactured water is supplied to the manufactured water tank 6 via line f.
After the water is stored in the tank, it is sent from line gK to processes that require manufactured water. At this time, line m middle extension 15 is closed. On the other hand, the concentrated water is discharged to the outside of the yarn through line 1.

Next, the cleaning of the membrane will be explained.

During cleaning, line d' middle extension 10 and line m middle extension 15 are opened, and line d middle extension 11 and line f middle extension 14 are closed.

The cleaning method of the present invention causes a forward osmosis phenomenon on the front and back surfaces of the membrane, and after the contaminated layer formed on the outer surface of the membrane is peeled off by permeated water, it is discharged to the outside of the membrane module along with the high solute concentration liquid flowing on the outer surface of the membrane. Therefore, it is necessary to supply a low solute concentration solution and a high solute concentration solution to the membrane module.

In this example, we will explain the case where raw water is used as the high solute concentration liquid and manufactured water is used as the low solute concentration liquid. It can be applied as long as it has no effect (for example, there is no clogging due to suspended matter).

Raw water to be a high solute concentration liquid is sent from the raw water tank 1 to the supply pump 2 via 2-in-b, and then sent to the filter 3 by the supply pump 2. After removing suspended matter and dead microorganisms from the raw water in the filter 3, the raw water is supplied to the membrane module 5 via line d' and line e, which are bypass lines thereof, without passing through the high-pressure pump 4.

On the other hand, the water that becomes the low solute concentration liquid is supplied from the manufactured water tank 6 to the membrane module 5 via the line m. Within the membrane module 5, permeated water moves from the inside of the membrane to the outside of the membrane, which is the raw water supply side, due to the forward osmosis phenomenon caused by the concentration difference. At this time, the contaminant layer adhering to the outer surface of the membrane is peeled off, and the concentrated water is extracted from the membrane module 5 through the concentrated water discharge line 1 and discharged to the outside of the system together with the raw water and permeated water.

As described above, according to the method of this embodiment, no special equipment or cleaning agent is required for membrane cleaning, and there is no need for a process for treating wastewater generated by membrane cleaning.

〔Effect of the invention〕

According to the method of the present invention, there is almost no need for special new equipment for cleaning reverse osmosis membranes, and equipment costs are reduced. Further, there is no need for cleaning agents, and there is no need for a process to treat the waste water generated when cleaning the reverse osmosis membrane, resulting in labor and energy savings.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the method of the present invention, and FIG. 2 is an explanatory diagram of a conventional reverse osmosis membrane cleaning method.

Claims (1)

[Claims] In a reverse osmosis device that desalinates water or reuses wastewater using a reverse osmosis membrane, a solution with a low solute concentration is supplied to the permeated water side of the reverse osmosis membrane, while a solution with a high solute concentration is supplied to the raw water side of the reverse osmosis membrane. A method for cleaning a reverse osmosis membrane, comprising supplying a liquid and removing a contaminated layer on the surface of the reverse osmosis membrane by a flow that passes through the reverse osmosis membrane based on a forward osmosis phenomenon that occurs through the reverse osmosis membrane.